Photoelectric cell



y 1940. A. KUBITZEK 2,206,196

PHOTOELECTRIC CELL I Filed Nov. 12, 1938 2 Shaets-Sheet 1.

July 2, 1940. A. KUBITZEK PHOTOELECTRIC CELL FiledNov. 12, 1938 2 Shady-Sheet 2 fizb erdvf 5! red KzLZIL't ek' atented July 2, 1940 V UNITED STATES. PATENT OFFICE PHOTOELECTBIC CELL Alfred Knbitaek, Dresden-Lanbcgast, Germany,

ngesellsc alsignor to Zeiss Ikon Aktie Dresden, Germany Application V In 3 Claims.

This invention relates to improvements in aotoelectric cells.

It is an object of the invention to provide a aotoelectric cell in which the range of the angle F incident rays of light energizing the cell is limited range. It has been known to restrict the range of the igle of rays of light adapted to energize a aotoelectric element by mechanicalor optical ,eans. In the utilization of optical means for miting the angle of incident rays, it had been roposedheretofore to direct away from the :11 by total reflection rays of light which re outside the deslredangle of incidence.

Where mechanical means were provided, they insisted of opaque ribs or projections suitably laced from each other, and thereby confining 1e angle of incidence to certain limits.

The optical andmechanical means heretofore sed, however, have the disadvantage that the inge of the angle of incidence still is excessive. 1 photographic work this range even though :stricted by optical or mechanical means, is reater than the picture'angle of the ordinary hotographic camera. Hence, the results indiited by the photometer. of which the photo- .ectric cell forms a part, are frequently not i agreement with the eflect of the light induclg the chemical reaction on the sensitized nulsion.

It is an object of the present invention to proide a photoelectric cell in which the'range of e, angle .of incidence of light affecting the all is limited to a greater degree than it had een feasible heretofore. g

It is also an object of the invention to bring bout this restriction of the range of the angle I incidence by causing the photoelectric cell to e energized by light which had repeatedly been eflected to strike the cell, while eliminating 1e influence of all other light by directing it way from. the cell.

'It is, therefore, also an object of the invention energize'through total reflection a photolectric cell solely by rays of a predetermined ngular inclinationto the cell.

The invention also has the object of energizig a photoelectric cell through indirect light nd particularly through light which has been ubjected to a repeated total reflection.

The invention also has the object of providig inassociation witha photoelectric cell one r more prisms disposed 'to the rear of the cell, be prism vor prisms preferably being'rectangu- 1r prisms and being adapted to direct the rays haft,

November 12, 19:8, Serial No. 240,156 Germany November 12, 193'! of light from forward of the cell by repeated total reflection to the sensitized layer of the cell averted from the light and protected against ordinary incident light by the carrier of the layer.

with these and numerous other objects in view, embodiments of the invention are described in the following specification and illustrated in the accompanying drawings.

In the drawings: I

Fig. 1 shows diagrammatically and partly in section a photometer having a photoelectric cell and means forrestricting the range of the effective angle of incidence in accordance with the present invention;

V Fig. 2 shows partly in section the photoelectric cell of Fig. 1 with a prism arrangement adapted to direct primarily rays of light against the cell which are atsubstantially right angle to the plane of the cell; i

Fig. 3 is a top plan view of an annular prism having a right angle triangular cross-section;

,Fig. 4 shows partly in section diagrammatically a photoelectric cell with a pair of prisms adapted to restrict the range of'the angle of incidence of energizing light, and

Fig. 5 is a top plan view of the assembly illustrated in P18. 4.

In the embodiment illustrated in Fig. 1, an

' electric photometer is shown diagrammatically. Its cell consists of a carrier or backing 2 with the layer 3 podtioned on the rear face of the carrier, which rear face is directed away from the light. The layer 3 is adapted to be electrically influenced by light striking the same, so as for instance to generate a greater or smaller current depending on the intensity of the light. This cell is combined with an electric instrument 4 diagrammatically indicated and of known construction, and with a variable resistance 5 through which the deflection of the instrument 4 may be selectively regulated. Photoelectric meters of this general construction are well known.

The carrier or backing 2 of the sensitized layer 3 is constructed as a plate and the sensitized layer faces the base A of an annular prism disposed in a plane parallel to the carrier 2 and having a right angle as prismatic deflecting angle. This base surface A projects beyond the contour of the cell.

In Figs. 1 and 2, the paths of raysof light entering the base surface A of the prism are indicated. It will be seen that light energizing the layer 3 of the photoelectric cell is twice reflected in the prism I, provided the rays of light enter the surface A at a substantially right angle thereto. Solely rays of light within a certain range of the angle of incidence can be repeatedly reflected to strike the layer 3. Rays of light striking this surface under different angles, as shown at b and c in Fig. 2, pass through the prism after being suitably refracted, and do not encounter the sensitized layer 3. The ray 2), after having struck the base surface A of the prism I, continues into the air after having passed through the prism, while the rays c are twice reflected within the body of the prism, but continue without encountering the layer Set the photoelectric cell. Hence, it is only the rays of light striking the base surface of the conical prism i within a certain range of a right angle, .or an angle closely related to a right angle, which become effective upon the photoelectric cell, while the other rays are directed away.

In the embodiment illustrated in Figs. 4 and 5, the annular conical prism is replaced by two prismatic bars 6 and I of triangular cross-section and having a right angle at the apex. These bars 6, l are positioned parallel to each other advisably with their bases B, C in a common plane parallel to the plane of the sensitized layer 3 applied to the carrier 2' of the photoelectric cell. The carrier faces forward toward the natural light; the layer 3' faces rearward. Here also the rays of light indicated at a and striking the base B under a right angle (or approximately so) are twice totally reflected to be directed towards the face of the cell averted from the direct light, and protected by the backing 2', while rays b and c striking the base of the prisms under an angle smaller or greater than the said range are deflected away from said cell. 7

The embodiment illustrated in Figs. '4 and 5 has the advantage that the carrier 2' of the layer 3' may be made in the form of a rectangular plate. I claim:

1. In combination with a photoelectric cell mounted on the rear face of a carrier plate which angularly positioned with respect to each other and with respect to the plane .of said photoelectric cell so that only light rays which enter said prism within a predetermined range of angle of incidence with respect to the plane of said cell are reflected to said photoelectric cell.

2. In combination with a photoelectriccell mounted on the rear face of a circular; carrier plate which protects the cell against light rays striking the front face of said plate, an annular right-angle prism positioned with its base adja cent and parallel to 'said'photoelectric cell and projecting beyond the contour of said circular plate so that only light rays entering the prism through the projecting portion of its base within a predetermined range of angles of incidence are twice totally reflected within said prism before they reach said photoelectric cell.

3. In combination with a photoelectric cell mounted on the rear face of a rectangular carrier plate which protects the cell against light rays striking the front face of said plate, a pair of prism bars of right-angle triangular cross-section positioned with their bases adjacent and parallel to said photoelectric 'cell, said prisms projecting a 

